Construction of two new photoluminescent coordination polymers via 5-position substituted 1,3-benzenedicarboxylate

Article abstract of DOI:10.1080/00958972.2012.731048

Two coordination polymers, [Cd(L1)(bib)]_n (1) and [Cd(L2)(bib)_0.5]_n (2) [H₂L1=5- hydroxyisophthalic acid, H₂L2=5-methylisophthalic acid and bib=1,4-bis(2-methyl-imidazol-1- yl)butane], have been synthesized and characterized by IR, elemental analysis, and X-ray diffraction. Compound 1 shows a 2-D layer structure and 2 is a two-fold interpenetrated 3-D pcu topology. The results suggest that the 5-position group affects the structure of coordination polymers. Luminescence properties of 1 and 2 are investigated.

Full text of DOI:10.1080/00958972.2012.731048

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Construction of two new photoluminescent
coordination polymers via 5-position substituted
1,3-benzenedicarboxylate
Feng Guo
To cite this article: Feng Guo (2012) Construction of two new photoluminescent coordination
polymers via 5-position substituted 1,3-benzenedicarboxylate, Journal of Coordination
Chemistry, 65:22, 4005-4012, DOI: 10.1080/00958972.2012.731048
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Date: 11 June 2016, At: 10:46

Journal of Coordination Chemistry
Vol. 65, No. 22, 20 November 2012, 4005–4012
Construction of two new photoluminescent coordination
polymers via 5-position substituted 1,3-benzenedicarboxylate
FENG GUO*
Key Laboratory of Coordination Chemistry and Functional Materials in
Universities of Shandong, Dezhou, Shandong 253023, P.R. China
(Received 11 March 2012; in final form 27 August 2012)
Two coordination polymers, [Cd(L1)(bib)]n (1) and [Cd(L2)(bib)0.5]n
(2) [H2L1 ¼ 5-hydro-
xyisophthalic acid, H2L2 ¼ 5-methylisophthalic acid and bib ¼ 1,4-bis(2-methyl-imidazol-1-
yl)butane], have been synthesized and characterized by IR, elemental analysis, and X-ray
diffraction. Compound 1 shows a 2-D layer structure and 2 is a two-fold interpenetrated 3-D
pcu topology. The results suggest that the 5-position group affects the structure of coordination
polymers. Luminescence properties of 1 and 2 are investigated.
Keywords: Coordination polymer; Crystal structure; Photoluminescence
1. Introduction
Metal–organic frameworks (MOFs) are currently of interest due to diverse structures
and potential applications in gas storage, magnetism, catalysis, and luminescence
[1–17]. Although rapid progress in MOFs has been made, it remains a challenge to
control the structures and composition of target products in crystal engineering.
Construction of MOFs is influenced by both structural and experimental factors, such
as ligands, pH, temperature, and solvents [16–19]. The most effective and facile method
to construct MOFs is choice of well-designed ligands containing modifiable backbones.
Combination of carboxylates with N-donor auxiliary ligands is a good choice for the
construction of new coordination polymers because of the varieties in coordination
modes of carboxylate [20–23]. Different non-coordinating groups in the 5-position
of 1,3-benzenedicarboxylate can generate different polymers [24]. Bis(imidazole) with
–CH2– spacers are good N-donor bridging ligands. The flexible nature of –CH2–
spacers allows the ligands to bend and rotate freely when coordinating to metal centers
to conform to the coordination geometries of metal ions [25–27].
Our work is devoted to the construction of MOFs through tuning the 5-position of
1,3-benzenedicarboxylate to study the effect on the MOFs. In this article, we use
5-hydroxyisophthalic acid, 5-methylisophthalic acid, and bib [1,4-bis(2-methyl-imida-
zol-1-yl) butane] as N-donor to synthesize two Cd(II) complexes. The results reveal that
*Email: guofeng1510@yeah.net
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.731048

4006
F. Guo
5-position group affects the structure of coordination polymers, changing from 2-D
layer structure to 3-D pcu network.
2. Experimental
2.1. Materials and physical measurements
All reagents and solvents were commercially available and used as received. Elemental
analysis was carried out on a Carlo Erba 1106 full-automatic trace organic elemental
analyzer. FT-IR spectra were recorded with a Bruker Equinox 55 FT-IR spectrometer
as a KBr pellet from 400 to 4000 cmꢀ1. Solid-state fluorescence spectra were recorded
on a Hitachi F-4600 equipped with a xenon lamp and a quartz carrier at room
temperature. X-ray powder diffraction (XRPD) measurements were performed on a
Bruker D8 diffractometer operated at 40 kV and 40 mA using Cu-Ka radiation
(ꢀ ¼ 0.15418 nm).
2.2. Syntheses
2.2.1. [Cd(L1)(bib)]n (1). A mixture of Cd(OAc)2 ꢁ 4H2O (0.308 g, 1 mmol), H2L1
(0.182 g, 1 mmol), bib (0.218 g, 1 mmol), NaOH (0.08 g, 2 mmol), and deionized water
(18 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 160ꢂC for
96 h. After cooling to room temperature, colorless block crystals were obtained and
washed with alcohol several times (yield: 42% based on Cd). Elemental Anal. Calcd for
C20H22CdN4O5 (%): C, 47.02; H, 4.34; N, 10.97. Found (%): C, 47.24; H, 4.28;
N, 11.30. IR: 1605 s, 1487 s, 1428 m, 1351 m, 1237 m, 1157 m, 924 m, 857 m, 742 m.
2.2.2. [Cd(L2)(bib)0.5]n (2). Compound 2 was obtained by hydrothermal procedure as
for preparation of 1 only using 5-methylisophthalic acid (0.180 g, 0.1 mmol) instead of
5-hydroxyisophthalic acid. Colorless block crystals of 2 were collected in 40% yield
based on Cd after washing by ethanol several times. Elemental Anal. Calcd for
C15H15CdN2O4 (%): C, 45.07; H, 3.78; N, 7.01. Found (%): C, 45.24; H, 3.75; N, 7.04.
IR: 1655 s, 1524 s, 1462 s, 1307 m, 1278 w, 10 971m, 904 m, 841 w, 754 m.
2.3. X-ray crystallography
Diffraction intensity data of the single crystals of 1 and 2 were collected on a Bruker
SMART APEX II CCD diffractometer equipped with graphite monochromated
˚
Mo-Ka radiation (ꢀ ¼ 0.71073 A) by using a !-scan mode. Empirical absorption
correction was applied using SADABS [28]. The structures were solved by direct
methods and refined by full-matrix least-squares on F2 using SHEXL 97 [29]. All non-
hydrogen atoms were refined anisotropically; hydrogen atoms were located geometri-
cally and their positions and thermal parameters were fixed during structure refinement.
Crystallographic data are summarized in table 1 with relevant bond lengths and angles
listed in table 2.

Photoluminescent coordination polymers
4007
Table 1. Crystallographic data and structure refinement summary for 1 and 2.
Empirical formula
Formula weight
Crystal system
Space group
C
510.82
Monoclinic
P21/n
20H22CdN4O5
C15H15CdN2O4
366.69
Monoclinic
P21/n
ꢂ
˚
Unit cell dimensions (A, )
a
b
c
9.131(2)
20.516(4)
11.364(3)
104.588(3)
2060.5(15), 4
1.545
9.345(4)
12.133(5)
13.349 (5)
91.948 (5)
1512.7(11), 4
1.755
ꢁ
Volume (A ), Z
3
˚
Calculated density (Mg mꢀ3
)
Independent reflections [I 4 2ꢂ(I)]
F(000)
3286
1032
3144
796
ꢃ range for data collection
Limiting indices
2.51–28.59
ꢀ10 ꢃ h ꢃ 10;
ꢀ24 ꢃ k ꢃ 18;
ꢀ24 ꢃ l ꢃ 18
1.083
R1 ¼ 0.0219
wR2 ¼ 0.0502
R1 ¼ 0.0252
wR2 ¼ 0.0520
0.282 and ꢀ0.314
2.27–27.54
ꢀ12 ꢃ h ꢃ 8;
ꢀ15 ꢃ k ꢃ 15;
ꢀ12 ꢃ l ꢃ 17
1.016
R1 ¼ 0.0206
wR2 ¼ 0.0524
R1 ¼ 0.0236
wR2 ¼ 0.0543
0.650 and ꢀ0.263
Goodness-of-fit on F2
Ra1, wRb1 [I 4 2ꢂ(I)]
Ra1, wRb1 (all data)
ꢀ3
˚
Largest difference peak and hole (e A
)
b
2
2 2
aR ¼ Æ(jjFoj ꢀ jFcjj)/ÆjFoj. wR ¼ [Æw(jFoj ꢀ jFcj ) /Æw(Fo2)]1/2
.
ꢂ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1 and 2.
Compound 1
Cd (1)–N(1)
Cd(1)–N(3)
2.259(2)
2.2596(19)
2.2941(19)
92.70(7)
140.50(7)
109.94(8)
124.24(8)
89.75(6)
Cd(1)–O(4)
Cd(1)–O(5)
2.323(2)
2.4044(17)
2.4915(18)
88.87(6)
Cd(1)–O(1)i
Cd(1)–O(2)i
N(1)–Cd(1)–N(3)
N(1)–Cd(1)–O(1)i
N(3)–Cd(1)–O(1)i
N(1)–Cd(1)–O(4)
N(3)–Cd(1)–O(4)
N(1)–Cd(1)–O(2)i
N(3)–Cd(1)–O(2)i
O(1)i–Cd(1)–O(2)i
O(1)i–Cd(1)–O(4)
N(1)–Cd(1)–O(5)
N(3)–Cd(1)–O(5)
O(1)i–Cd(1)–O(5)
O(4)–Cd(1)–O(5)
O(4)–Cd(1)–O(2)i
O(5)–Cd(1)–O(2)i
94.08(7)
141.33(7)
87.91(7)
55.52(6)
141.05(6)
105.59(7)
87.53(7)
112.71(7)
54.28(6)
Compound 2
Cd(1)–N(1)
2.2061(17)
2.2652(15)
105.80(6)
94.12(6)
152.53(6)
105.53(7)
76.55(7)
109.28(7)
86.91(6)
104.43(7)
Cd(1)–O(4)ii
2.2745(15)
2.3436(17)
80.04(7)
162.34(7)
81.71 (6)
84.82(6)
91.68(5)
144.39(6)
54.41(6)
Cd(1)–O(3)i
Cd(1)–O(1)iii
N(1)–Cd(1)–O(3)i
N(1)–Cd(1)–O(4)ii
O(3)i–Cd(1)–O(4)ii
N(1)–Cd(1)–O(1)iii
O(3)i–Cd(1)–O(1)iii
N(1)–Cd(1)–O(2)
O(3)i–Cd(1)–O(2)
O(4)ii–Cd(1)–O(2)
O(4)ii–Cd(1)–O(1)iii
N(1)–Cd(1)–O(1A)
O(3)i–Cd(1)–O(1A)
O(4)ii–Cd(1)–O(1A)
O(1)iii–Cd(1)–O(1A)
O(1)iii–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
i
i
ii
Symmetry codes: for 1: x ꢀ 1/2, ꢀy þ 1/2, z þ 1/2; for 2: ꢀx þ 1/2, y ꢀ 1/2, ꢀz þ 1/2; x ꢀ 1/2, ꢀy þ 3/2,
iii
z þ 1/2; ꢀx, ꢀy þ 1, ꢀz þ 1.

4008
F. Guo
3. Results and discussion
3.1. Description of crystal structures
3.1.1. Cd(L1)(bib)]n (1). X-ray diffraction analysis revealed that [Cd(L1)(bib)]n (1)
consists of one Cd(II), one L1, and one bib. Each CdII is six-coordinate by four oxygen
atoms from L1 [Cd(1)–O(1) ¼ 2.294(19), Cd(1)–O(2) ¼ 2.492(18), Cd(1)–O(4) ¼
˚
2.323(2), and Cd(1)–O(5) ¼ 2.404(14) A] and two nitrogen atoms from two bib ligands
˚
[Cd(1)–N(1) ¼ 2.259(2) and Cd(1)–N(3) ¼ 2.260(19) A], showing a distorted octahedral
geometry (figure 1a). Each L1 adopts a bis-chelating mode to link adjacent Cd’s to form
1-D chains, which are further connected by bib to form a 2-D layer (figure 1b). The 2-D
layers are further assembled by intermolecular hydrogen bonds with a H(21)ꢁ ꢁ ꢁO(2)
ꢂ
˚
distance of 1.89 A and the angle of 168 [O(3)–H(21)ꢁ ꢁ ꢁO(2)], leading to formation of a
3-D framework (figure 1c).
Considering the hydrogen-bonding interaction, L1 can be simplified as a three-
connected node; Cd(II) can be regarded as a four-connected node. In this method, the
3-D supramolecular structure can be rationalized as a (3,4)-connected InS net with a
Schafli symbol of (63) ꢁ (65 ꢁ 8), which is the first example of an InS net formed via
¨
hydrogen-bonding interactions (figure 1d).
3.1.2. [Cd(L2)(bib)0.5]n (2). In [Cd(L2)(bib)0.5]n (2), each CdII is also six-coordinate by
˚
five oxygen atoms from L2 [Cd–O bond lengths varying from 2.265(15) to 2.404(16) A]
˚
and one nitrogen atom from one bib [Cd(1)–N(1) ¼ 2.206(17) A], showing a distorted
Figure 1. (a) Coordination environment of Cd(II) in 1. Hydrogen atoms are omitted for clarity; (b) the 2-D
layer structure; (c) 3-D supramolecular structure via hydrogen bonds; and (d) the InS network of the
(63) ꢁ (65 ꢁ 8) topology for the 3-D supramolecular structure.

Photoluminescent coordination polymers
4009
octahedral geometry (figure 2a). Each L2 is bis-monodentate and chelating/bridging
˚
modes, forming a binuclear Cd unit (dCd–Cd ¼ 3.280 A). The dimers are bonded to four
L2 and thus can be regarded as a four-connected node to generate a (4,4) 2-D layer
(figure 2b). The 2-D layers are further bridged by bib to generate a 3-D framework.
From a topological view, the dimeric unit can be treated as a six-connected node with
L2 and bib as linkers; the 3-D structure can be classified as a pcu-related net (ꢄ-Po
topology). Due to the absence of guest molecules to fill the large void space in the 3-D
framework during assembly, the potential voids in 2 are filled via mutual interpene-
tration of two identical 3-D nets, which directly leads to formation of a two-fold
interpenetrated network (figure 2c).
3.2. X-ray powder diffraction
XRPD was used to confirm the phase purity of bulk materials of 1 and 2 at room
temperature, indicating that the synthesized 1 and 2 are homogeneous systems
(figure S1, Supplementary material).
3.3. Photoluminescent properties
Luminescent properties of 1 and 2 were investigated in the solid state at room
temperature. Complexes 1 and 2 exhibit fluorescent emission bands with maxima at
Figure 2. (a) Coordination environment of Cd(II) in 2. Hydrogen atoms and free water are omitted for
clarity; (b) the 2-D layer formed by carboxylates; and (c) the two-fold interpenetrated pcu net.

4010
F. Guo
Figure 3. Solid-state emission spectra of 1 and 2 at room temperature.
386 nm and 409 nm upon excitation at 334 nm and 340 nm, respectively. To understand
the nature of these emissions, we compared the emission spectra of the two compounds
and those of free H2L1, H2L2, and bib which exhibit broad weak fluorescent emission
centered on 350 nm (ꢀex ¼ 280 nm) [24], 380 nm (ꢀex ¼ 280 nm) [30], and 465 nm
(ꢀex ¼ 280 nm) [31] (figure 3). The emissions of 1 and 2 are tentatively assigned to
intraligand transition due to their similarity to ligands. Cd is difficult to oxidize or
reduce [32–34]. The different emission positions and intensities of 1 and 2 may be due to
the different structures because enhancement of luminescence is associated with
coordination of ligands to metal [35, 36].
4. Conclusion
We synthesized two new coordination polymers. Compound 1 shows a 3-D supramo-
lecular structure with InS topology via hydrogen bonds. Compound 2 is a two-fold pcu
topology. Changing the 5-position substituent, the structures from a 2-D net into a 3-D
framework affects the structure of coordination polymers. In comparison with 1 and 2,
using the same N-donor ligand, the carboxylates have a critical impact on the
construction of different MOFs due to their steric and/or electronic effect at the
5-position. When –OH is changed to –CH3, the structures are changed from 2-D layer
to 3-D pcu network. Compounds 1 and 2 also exhibit emission in the solid state at room
temperature.
Supplementary material
Crystallographic data for the structural analysis have been deposited with the
Cambridge Crystallographic Data Center, CCDC reference numbers: 862572

Photoluminescent coordination polymers
4011
and 862573. These data can be obtained free of charge at http://www.ccdc.cam.ac.uk or
Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: þ44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk).
Acknowledgments
We acknowledge the support of this work by The Natural Science Foundation of
Shandong Province (ZR2011BL024) and the financial support from Dezhou University
(318019).
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